1. Technical Field
The present disclosure relates to devices for interfacing with high frequency data transfer media and, more particularly, to insulation displacement contact (xe2x80x9cIDCxe2x80x9d) devices, such as those that are used as interface connectors for Unshielded Twisted Pair (xe2x80x9cUTPxe2x80x9d) media, that advantageously compensate for and reduce electrical noise.
2. Background Art
In data transmission, the signal originally transmitted through the data transfer media is not necessarily the signal received. The received signal will consist of the original signal after being modified by various distortions and additional unwanted signals that affect the original signal between transmission and reception. These distortions and unwanted signals are commonly collectively referred to as xe2x80x9celectrical noise,xe2x80x9d or simply xe2x80x9cnoise.xe2x80x9d Noise is a primary limiting factor in the performance of a communication system. Many problems may arise from the existence of noise in connection with data transmissions, such as data errors, system malfunctions and/or loss of the intended signals.
The transmission of data, by itself, generally causes unwanted noise. Such internally generated noise arises from electromagnetic energy that is induced by the electrical energy in the individual signal-carrying lines within the data transfer media and/or data transfer connecting devices, such electromagnetic energy radiating onto or toward adjacent lines in the same media or device. This cross coupling of electromagnetic energy (i.e., electromagnetic interference or EMI) from a xe2x80x9csourcexe2x80x9d line to a xe2x80x9cvictimxe2x80x9d line is generally referred to as xe2x80x9ccrosstalk.xe2x80x9d
Most data transfer media consist of multiple pairs of lines bundled together. Communication systems typically incorporate many such media and connectors for data transfer. Thus, there inherently exists an opportunity for significant crosstalk interference.
Crosstalk can be categorized in one of two forms. Near end crosstalk, commonly referred to as NEXT, arises from the effects of near field capacitive (electrostatic) and inductive (magnetic) coupling between source and victim electrical transmissions. NEXT increases the additive noise at the receiver and therefore degrades the signal to noise ratio (SNR). NEXT is generally the most significant form of crosstalk because the high-energy signal from an adjacent line can induce relatively significant crosstalk into the primary signal. The other form of crosstalk is far end crosstalk, or FEXT, which arises due to capacitive and inductive coupling between the source and victim electrical devices at the far end (or opposite end) of the transmission path. FEXT is typically less of an issue because the far end interfering signal is attenuated as it traverses the loop.
Characteristics and parameters associated with electromagnetic energy waves can be derived by Maxwell""s wave equations. In unbounded free space, a sinusoidal disturbance propagates as a transverse electromagnetic wave. This means that the electric field vectors are perpendicular to the magnetic field vectors lying in a plane perpendicular to the direction of the wave. As a result, crosstalk generally gives rise to a waveform shaped differently than the individual waveform(s) originally transmitted.
Unshielded Twisted Pair cable or UTP is a popular and widely used type of data transfer media. UTP is a very flexible, low cost media, and can be used for either voice or data communications. In fact, UTP is rapidly becoming the defacto standard for Local Area Networks (xe2x80x9cLANsxe2x80x9d) and other in-building voice and data communications applications. In a UTP, a pair of copper wires generally form the twisted pair. For example, a pair of copper wires with diameters of 0.4-0.8 mm may be twisted together and wrapped with a plastic coating to form a UTP. The twisting of the wires increases the noise immunity and reduces the bit error rate (BER) of the data transmission to some degree. Also, using two wires, rather than one, to carry each signal permits differential signaling to be used. Differential signaling is generally more immune to the effects of external electrical noise.
The non-use of cable shielding (e.g., a foil or braided metallic covering) in fabricating UTP generally increases the effects of outside interference, but also results in reduced cost, size, and installation time of the cable and associated connectors. Additionally, non-use of cable shielding in UTP fabrication generally eliminates the possibility of ground loops (i.e., current flowing in the shield because of the ground voltage at each end of the cable not being exactly the same). Ground loops may give rise to a current that induces interference within the cable, interference against which the shield was intended to protect.
The wide acceptance and use of UTP for data and voice transmission is primarily due to the large installed base, low cost and ease of new installation. Another important feature of UTP is that it can be used for varied applications, such as for Ethernet, Token Ring, FDDI, ATM, EIA-232, ISDN, analog telephone (POTS), and other types of communication. This flexibility allows the same type of cable/system components (such as data jacks, plugs, cross-patch panels, and patch cables) to be used for an entire building, unlike shielded twisted pair media (xe2x80x9cSTPxe2x80x9d).
At present, UTP is being used for systems having increasingly higher data rates. Since demands on networks using UTP systems (e.g., 100 Mbit/s and 1200 Mbit/s transmission rates) have increased, it has become necessary to develop industry standards for higher system bandwidth performance. Systems and installations that began as simple analog telephone service and low speed network systems have now become high speed data systems. As the speeds have increased, so too has the noise.
The ANSI/TIA/EIA 568A standard defines electrical performance for systems that utilize the 1 to 100 MHz frequency bandwidth range. Exemplary data systems that utilize the 1-100 MHz frequency bandwidth range include IEEE Token Ring, Ethernet10Base-T and 100Base-T. EIA/TIA-568 and the subsequent TSB-36 standards define five categories, as shown in the following Table, for quantifying the quality of the cable (for example, only Categories 3, 4, and 5 are considered xe2x80x9cdatagrade UTPxe2x80x9d).
Underwriter""s Laboratory defines a level-based system, which has minor differences relative to the EIA/TIA-568xe2x80x2s category system. For example, UL requires the characteristics to be measured at various temperatures. However, generally (for example), UL Level V (Roman numerals are used) is the same as EIA""s Category 5, and cables are usually marked with both EIA and UL rating designations.
UTP cable standards are also specified in the EIA/TIA-568 Commercial Building Telecommunications Wiring Standard, including the electrical and physical requirements for UTP, STP, coaxial cables, and optical fiber cables. For UTP, the requirements currently include:
Four individually twisted pairs per cable
Each pair has a characteristic impedance of 100 Ohms+/xe2x88x9215% (when measured at frequencies of 1 to 16 MHz)
24 gauge (0.5106-mm-diameter) or optionally 22 gauge (0.6438 mm diameter) copper conductors are used
Additionally, the EIA/TIA-568 standard specifies the color coding, cable diameter, and other electrical characteristics, such as the maximum cross-talk (i.e., how much a signal in one pair interferes with the signal in another pairxe2x80x94through capacitive, inductive, and other types of coupling). Since this functional property is measured as how many decibels (dB) quieter the induced signal is than the original interfering signal, larger numbers reflect better performance.
Category 5 cabling systems generally provide adequate NEXT margins to allow for the high NEXT associated with use of present UTP system components. Demands for higher frequencies, more bandwidth and improved systems (e.g., Ethernet 1000Base-T) on UTP cabling, render existing systems and methods unacceptable. The TIA/EIA category 6 draft addendum related to new category 6 cabling standards illustrates heightened performance demands. For frequency bandwidths of 1 to 250 MHz, the draft addendum requires the minimum NEXT values at 100 MHz to be xe2x88x9239.9 dB and xe2x88x9233.1 dB at 250 MHz for a channel link, and xe2x88x9254 dB at 100 MHz and xe2x88x9246 dB at 250 MHz for connecting hardware. Increasing the bandwidth for new category 6 (i.e., from 1 to 100 MHz in category 5 to 1 to 250 MHz in category 6) increases the need to review opportunities for further reducing system noise.
The standard IDC terminal block is configured and dimensioned so as to provide maximum compatibility and matability between various manufacturers, e.g., based on the standard for 110C connecting block mechanical dimensions. Two types of offsets have been produced from the standard 110C connecting block dimensions.
Type one is the standard 110C connecting block style for UTP cable splicing which is a straight through contact design and does not add any compensation methods to reduce crosstalk noises. The standard 110C connecting block provides a straightforward approach for 110C connecting block, by alignment of lead frames is in an uniformed parallel pattern high NEXT and FEXT is produced for certain wire pairs that are side by side. The standard 110C connecting block style is defined by two lead frame wire electrical connecting areas, section one is the matable area for input wire contact and section two is the output wire contact which completes the electrical signal connecting. This alignment of lead frames in an uniformed parallel pattern produces increases in NEXT and FEXT noises as well as increases in wire pair impedance.
Type two is the standard FCC part 68.500 style for modular plug housing which uses either pair separation or metal shielding methods to reduce crosstalk noises. Using either pair separation or metal shielding typically requires increasing the physical size from the IDC standard dimensions. Signal compensation is not needed by this approach since the wire pair separation of greater than 0.075 inches alone will decrease electrical NEXT noises by at least 9 dB. However, this method of reducing pair to pair NEXT does not re-balance the FEXT nor the impedance in the wires, since the pair capacitance has been offset by the IDC lead frames. If used, the metal shield is typically inserted between two wire pair lead frames to reduce the adjacent side of each wire pairs coupling to each other. These various methods provide a non-compensation approach for IDC terminal block NEXT reduction, but not without increasing IDC size and/or expensively re-bending extra metal coupling units to remove crosstalk noises.
Methods of compensation methods for connecting hardware crosstalk noise reduction and controlling are also addressed in U.S. Pat. No. 5,618,185 to Aekins, the subject matter of which is hereby incorporated herein by reference thereto.
In view of the increasing performance demands being placed on UTP systems, e.g., the implementation of category 6 standards, it would be beneficial to provide a device and/or methodology that reduces NEXT and FEXT noises associated with standard IDC terminal blocks in a simple and cost effective manner. These and other objectives are achieved through the advantageous insert devices and systems disclosed herein.
The present disclosure provides a device that reduces the crosstalk NEXT and FEXT noises in IDC terminal blocks for a data/voice communication systems. A printed circuit board (xe2x80x9cPCBxe2x80x9d) with the proper balance coupling is incorporated in the block to reduce noise and re-balance the signal without negatively impacting the impedance characteristics of the wire pairs in a simple and low cost manner. The electrical noise is reduced by the positional relationship of signals during passage through the PCB which advantageously results in signal feedback reactances that are used to compensate for pair to pair NEXT, FEXT and impedance.
In summary, the present disclosure is directed to providing a device for reducing electrical noise during the transfer of data signals between media having a plurality of electrically conductive signal carrying elements.
In one embodiment, the device includes a dielectric support member, a means for receiving and transmitting signals from the signal carrying elements and a means for using the signals themselves to produce a capacitance which reduces the electrical noise. In one aspect, the means for receiving and transmitting signals from the signal elements disposed on the support member is a plurality of electrically conductive ports in electrical communication with the signal elements. Additionally, the means for using the signals to produce a capacitance may take the form of a plurality of elongated electrically conductive members in a close positional relationship or pattern with respect to each other.
The present disclosure additionally embodies a device for reducing crosstalk noise in an insulation displacement contact connectable with media having a plurality of signal carrying elements with positive and negative polarity data signals. In one aspect, this embodiment includes a dielectric support member and a plurality of elongated electrically conductive members disposed on the support member. The conductive members are in electrical communication with the insulation displacement contact for receiving the data signals, and in a positional relationship with respect to each to produce a capacitance for reducing the crosstalk noise. Preferably, one or more elongated members are associated with only one signal carrying element. It is also preferable to have a greater amount of elongated members associated with signal carrying elements of like polarities to be in positional relationships which form a capacitance, rather than the elongated members associated with signal carrying elements of opposing polarities. The deliberate positioning of members of the same polarity to form a capacitance strengthens the respective signals in the members. Preferably, the elongated members are all substantially the same size and distance from each other.
In another embodiment, a system for reducing electrical noise during the transfer of data signals between media cables having signal carrying elements of negative and positive polarity is disclosed. The system includes an IDC in electrical communication with communication ports on a PCB. The ports are in turn in electrical communication with electrically conductive traces having portions in positional relationships with respect to each other for forming a capacitance to reduce electrical noise in the associated signals. Preferably, there are eight communication ports which corresponds with standard 4 pair (8 wires) UTP cables.
For purposes of further illustrating this particular embodiment, it is assumed that communication ports one through eight are in communication with wires one through eight in a standard UTP cable. Thus, the preferred arrangement is as follows: traces in communication with port three are in a positional relationship for forming a capacitance with traces in communication with port one and port five; traces in communication with port seven are in a positional relationship for forming a capacitance with traces in communication with port eight and port five; traces in communication with port six are in a positional relationship for forming a capacitance with traces in communication with port four and port eight; and traces in communication with port four are in a positional relationship for forming a capacitance with traces in communication with port one and port two.
Preferably, the arrangement of traces produce a balanced voltage bridge of mutual capacitor reactance to compensate for the electrical noise in the signals to the PCB.
These and other unique features of the systems, devices and methods of the present disclosure will become more readily apparent from the following description of the drawings taken in conjunction with the detailed description of preferred and exemplary embodiments.